Process for induction heating and quenching of metal



w. c.' RUDD Filed Jan. 27, 1958 PROCESS FOR INDUCTION HEATING ANDQUENCHING OF METAL @Ok TEMZU Q UZMS UUA lwemw March 29, 1960 mumso ENE 0mm rook QS q OEkZO HE United St e Pat n 9 PRocEss FOR INDUCTION HEATINGAND QUENCHING or METAL Wallace 0. Rudd, Larchmont, N.Y., assignor toMagnetic Heating Corp., New Rochelle, N.Y., a corporation of New YorkApplication January 27, 1958, Serial No. 711,357

2 Claims. (Cl. 148-150) This invention relates to the heat treating ofmetal members or objects by electromagnetic induction, the in ventionamong other possibilities being particularly adapted for the heattreating to a desired limited depth of spaced-apart areas on metalobjects such as 'wires, strips or the like which are advanced throughthe apparatus.

The invention, for example, has been found to be well adapted for thesurface hardening of spaced-apart areas on wire, such that the treatedwire at points between the hardened areas may be cut into separatelengths each having soft ends but with surface-hardened midportions. Thethus formed separate pieces of the treated wire may be used as pins, forexample in the manufacture of certain types of chain, in which it isdesired to have the" main body portion of the pin surfacehardened, whileleaving the ends soft so that they may be peened over to hold the pinsin place in use. The forming of such pins heretofore has commonly beenaccomplished by carburizing the stock, plating it where it is notdesired that it be hardened, and then going through an involved andexpensive series of steps to secure the desired product.

One of the problems of such surface-hardening of metal, particularly ifthe hardening is to extend only to a predetermined shallow depth and theobject is not large in cross-section or diameter, arises from thenecessity of imparting to the object a great amount of heat rapidlyenough for heating the surfaces to the desired degree without heatingthe core of the metal to hardening temperature, and then almostimmediately quenching the metal object before the hardening temperaturepenetrates beyond the desired limited depth. And such problem be comeseven more difiicult where the metal object is to be surface-hardenedonly at predetermined. spaced areas, or where the objects are smallandinexpensive and for economy must be annealed uniformly in rapidsuccession.

In accordance with the present invention, these problems are overcome ina relatively simple and inexpensive way. For example, in a case where itis desired to form surface-hardened metal pins as above referred to,this may be done by longitudinally moving a wire of which the pins areto be formed stepby step so that spacedapart areas thereon will besuccessively positioned for a short interval in an induction'heatingarrangement as hereafter described, and-in which, afterquickly heatingthe desired 'areas, the same are immediately quenched and the treatedwire-is thereafter automatically advanced from the apparatus and cutinto lengths at points between the surface-hardened areas to form thepins with hardened surfaces at their mid-portions but with soft ends.Such induction heating arrangement in accordance with the'inventioncomprises an insulation tube through which a quenching fluid, such aswater, is caused to flow and, while the wire is passed in such quenchingfluid through the tube step by step, the tube being surrounded by a highfrequency induction heating coil of one or preferably several turns. Inthis way, the suc- 2,930,724 Patented Mar. 29, 1960 the quenching fluidwithin the tube and within the in-' duction heating coil, may be quicklyheated but in their surface portions only, by momentarily supplying theheating coil with high frequency current. This causes the cooling fluidwhich is flowing past the heated areas on the wire momentarily to becomevolatilized. That is, in case the cooling fluid is water, the heatedareas will immediately and momentarily be surrounded with substantiallyan envelope of steam, but this will condense'and collapse the moment theheating current is cut off, thereby causing the heated area to beimmediately quenched by the flowing stream, thus limiting thepenetration of the heat to the depth of the desired surface hardening,even before the wire is advanced the next step. As the treated wireemerges from the apparatus, it may be automatically cut into blanks atpoints intermediate the treated areas to form the desired pins.

With the form of the apparatus of the invention here shown, the wire orrod to be treated is advanced stageby-stage generally horizontallystraight through an insulation tube surrounded by an induction heatingcoil and containing the flowing stream of cooling liquid, the wirepassing through stuffing boxes where it enters and leaves the flowingstream. However, it will be understood that the apparatus may, takevarious other forms which may or may not require such stufling boxes andin which, for example, the wire may be advanced in a generally verticaldirection or be suitably supported to follow a curved path in theflowing stream. Also, the invention may be used for surface hardeningseparate elements carried through the apparatus on any suitable strandor the like.

Various further and more specific objects, features and advantages ofthe invention will appear from the description given below, taken inconnection with the accompanying drawings, illustrating by way ofexample a preferre form of the invention.

In the drawings:

Fig. l is a somewhat schematic perspective view of a presently preferredform of the apparatus for carrying out the invention;

Fig. 2 is a view, partly broken away, showing a section takensubstantially along the line 22 of Fig. 1;

Fig. 3 is a longitudinal sectional view of the treated wire; and

Fig. 4 is a sectional view taken along line 4--4 of" a shortpredetermined time and then similarly advancing it successively byadditional steps through the heating apparatus and finally to anysuitable known form of automatic cutting device as at 13 which will cutthe wire into desired lengths to form the pins.

An induction heating coil of several turns is-indicated at 14, this coilbeing preferably formed of hollow tubing for containing cooling liquid,as is customary for high fre: quencyinduction heating coils. The coil isconnected to I a high frequency generator of a suitable known type as at15, preferably of a type to supply current of a frequency of the orderof 100,000 cycles per second or higher, such as 450 kilocycles,; whichhas been found satisfactory in a typical case. 7

As indicated at 16, a suitable known form of timing device may beprovided with electrical connections to control the timing of theoperation of the indexing device 12 and also to control, in proper phaserelationship, a time-control switch as at 17, which in turn acts to turnon and shut off the high frequency current supply of the generator tothe coil 14. The timer as indicated may also be connected to control theactuations of the cutting-off device. If the generator is of the typeembodying oscillator tubes, the timer which may be a suitable known typeof electronic timer, may be connected to control the grids of theoscillator tubes so as to provide a very short period of current supplyamounting to a fraction of a second at the time when a surface area tobe heated on the wire is lodged within the heating coil.

The wire, in passing into the apparatus, may first pass through astuffing box, as at 18, mounted in a supporting bar 19. Thence the wirepasses on through a length of tubing 2%, preferably, although notnecessarily, formed entirely of insulating material such for example aspolytetrafluorethylene, the wire then passing on through anothersupporting bar 21 containing the outlet and a like stuffing box. Coolingliquid such as water is introduced through an inlet as at 22 to passthrough a cavity as at 23 in the arm 19 and thence through the tube 20to a like cavity in the arm 21 and finally to an outlet tube 24. Thecooling liquid may be supplied at an adjustable pressure to permitsuitable adjustment of its velocity through the tube.

With this apparatus, various sizes of wire strips or rods may betreated, the equipment as shown being adapted for treatment of wire ofvarious sizes for example from one-tenth of an inch up to three-eighthsof an inch or more in diameter, the stufling boxes and tubing, ofcourse, being made of suitable sizes to accommodate members of suchdiameters. In a typical case, which has proven highly successful inoperation, a 50 kilowatt generator was used, providing current at afrequency of 450 kilocycles with the timer and time control switchadjusted to provide for a heating time of 0.05 second for a wire of adiameter of about 0.183". In this case, the depth of the surfacehardening was between about 0.03" and 0.05", with the length of theheated sections varying from fiveeighths inch to one inch or more. Theindexing device was so adjusted that the apparatus produced from aboutfifty to sixty heat-treated pieces per minute.

Fig. 3 is a sectional view through a piece of wire with the shaded areasshowing the portions which have been surface-hardened, Fig. 4 being across-section through one of such portions.

In operation, the indexing device is so adjusted as to advance thelength of the wire which is to be treated to a position within the coil14, whereupon the timer and time control switch are adjusted to turn onthe high frequency current for an interval of time on the order of 0.05second. With the above-indicated amount of power available, this causesthe wire surfaces within the coil to become immediately heated, althoughinitially surrounded with the flowing stream of cooling fluid. As thewire surface areas are almost immediately brought to the desiredtemperature, same will become substantially enveloped in steam, andsince steam is a good thermal insulator, only a small portion of theheat from the surface of the wire will be conducted away by the liquid,but the wire will promptly become heated to the desired depth, when thepower is shut off and thereupon immediately the steam envelope moves onand collapses so that the flowing cooling liquid quenches the heatedarea before sufficient time has elapsed for the penetration of heat togreater than the desired depth in the wire. The indexing device thenadvances the wire for another fixed distance, whereupon theabove-described operations are repeated. As above explained, the wire,upon emerging from the apparatus, or afterwards, may be cut into lengthsat the desired points to form pins or the like having the desiredportions hardened and with other portions still relatively soft.

With the arrangement as described, it will be apparent that it ispossible to subject the desired areas of heating to a great amount ofheat quickly and because of the envelope of stem which forms, theheating is highly efficient in that very little heat is conducted awaydespite the close proximity of the quenching fluid, and yet the heatingmay be interrupted so quickly and be so quickly followed by thequenching step, that the depth of penetration of the hardening islimited to the desired predetermined distance. Since, after the power iscut off, quenching follows immediately, this avoids any appreciablesoaking period which might be prohibitive, particularly for a relativelysmall wire, the core of which is not desired to be hardened.

Although a certain particular embodiment of the invention is hereindisclosed for purposes of explanation, further modifications thereof,after study of this specification, will be apparent to those skilled inthe art to which the invention pertains. Reference should accordingly behad to the appended claims in determining the scope of the invention.

What is claimed and desired to be secured by Letters Patent is:

1. Method for surface-hardening a succession of spaced areas on anelongated metal member by the use of high frequency induction heating,which method comprises: advancing such member in a succession of stepsto predetermined positions within a flowing stream of volatilizablecooling liquid; and subjecting each such area at one of said positionsmomentarily to a high frequency magnetic field of sufficient intensityquickly to heat only the surface thereof to hardening temperature, eachheated area acting to volatilize the liquid contacting therewith, thusmomentarily substantially covering same by a heat-insulating layer ofvolatilized liquid, which layer collapses due to the flowing of saidstream upon discontinuance of the field, thereby allowing each such areaimmediately to be quenched by such flowing stream.

2. Method for surface-hardening a succession of spaced areas on anelongated metal member by the use of high frequency induction heating,which method comprises: advancing such member in a succession of stepsto predetermined positions within a flowing stream of volatilizablecooling liquid; and subjecting each such area at one of said positionsmomentarily to a high frequency magnetic field of sufficient intensityquickly to heat each such area to hardening temperature but only to apredetermined depth, each heated area acting to volatilize the liquidcontacting therewith, thus momentarily substantially covering same by aheat-insulating layer of volatilized liquid, which layer collapses dueto the flowing of said stream upon discontinuance of the field, therebyallowing each such area immediately to be quenched by such flowingstream, thus preventing further penetration of the heat towards the coreof the member,

References Cited in the file of this patent UNITED STATES PATENTS Re.20,673 Meyers -.L Mar. l5, 1938 1,355,521 Alexander et al. Oct. 12, 19202,459,507 Denham Jan. 18, 1949 2,604,577 Strickland et al July 22, 1952FOREIGN PATENTS 461,935 Great Britain Feb. 26, 1937 OTHER REFERENCESIron Age, September 12, 1946. Page 76.

1. MET''OD FOR SURFACE-HARDENING A SUCCESSION OF SPACED AREAS ON ANELONGATED METAL MEMBER BY THE USE OF HIGH FREQUENCY INDUCTION HEATING,WHICH METHOD COMPRISES: ADVANCING SUCH MEMBER IN A SUCCESSION OF STEPSTO PREDETERMINED POSITIONS WITHIN A FLOWING STREAM OF VOLATIZABLECOOLING LIQUID? AND SUBJECTING EACH SUCH AREA AT ONE OF SAID POSITIONSMOMENTARILY TO A HIGH FREQUENCY MAGNETIC FIELD OF SUFFICIENT INTENSITYQUICKLY TO HEAT ONLY THE SURFACE THEREOF TO HARDENING TEMPERATURE, EACHHEATED AREA ACTING TO VOLATILIZE THE LIQUID CONTACTING THEREWITH, THUSMOMENTARILY SUBSTANTIALLY COVERING SAME BY A HEATING-INSULATING LAYER OFVOLATILIZED LIQUID, WHICH LAYER COLLAPSES DUE TO THE FLOWING OF SAIDSTREAM UPON DISCONTINUANCE OF THE FIELD, THEREBY ALLOWING EACH SUCH AREAIMMEDIATELY TO BE QUENCHED BY SUCH FLOWING STREAM.